In the semiconductor manufacturing process, oxide films such as a silicon oxide film (SiO2), etc. and nitride films such as a silicon nitride film (SiNx), etc. are used as typical insulating films, by which each of them is laminated or at least a film is alternately laminated. The silicon nitride film is in contacted with surfaces of a silicon oxide film, a polysilicon film, or a silicon wafer and is deposited via a CVD (Chemical Vapor Deposition) process and is removed by dry etching and wet etching. Among these etching using phosphoric acid is widely used.
In wet etching process for removing the silicon nitride film, a mixture of phosphoric acid and deionized water is generally used. The deionized water is added in order to prevent the decrease of the etch rate and the change of the etching selectivity to the oxide film, however there is a problem that defects are caused in the process of removing nitride film by etching even with a minute change in the amount of deionized water to be supplied. In addition, phosphoric add is corrosive as a strong acid and has difficulty in handling.
In order to solve this problem, there has been disclosed a method of removing a nitride film by using an etching composition containing hydrofluoric acid (HF) or nitric acid (HNO3) to phosphoric acid (H3PO4), however, rather, the etch rate of the oxide film increases and the etching selectivity of the nitride film and the oxide film is decreased.
In addition, a technique using trisilanol to lower the etch rate of the oxide film is disclosed, when trisilanol is used, there is a problem that many particles are generated after the etching process and the recycling of the phosphoric acid cannot possible.
The reason why particles are generated when trisilanol is used is that trisilanol groups in phosphoric acid react with each other to change into a Si—O—Si form and increase in size. At this time, it is desirable that the groups react to each other constantly and the particle size is uniform, but particles of various sizes are generated thereby generating particle size of at least 0.05 μm and greater than 200 μm. When the generated particles are deposited on a wafer, the wafer is defective.
Therefore, to overcome the above mentioned problems, there is a need to develop an etching composition having a new composition that prevents particles from being generated while selectively etching the silicon nitride film in respect of the silicon oxide film.